docs: def check_ratebase(self, rate):
          """Helper function"""
          split = rate['name'].partition('/')
          if split[1]:
              ratebase = split[0]
              if ratebase != self.base:
                  raise RuntimeError("%s: %s has different base rate:\n%s" % (
                      self.name, ratebase, rate))
          elif rate['name'] == self.base:
              pass
          # Codes beginning with 'X' are treated specially, e.g.
          # Gold (XAU), Copper (XCP), Palladium (XPD), Platinum (XPT), Silver (XAG)
          # They still appear to be based on USD but are reported with no base
          elif not rate['symbol'].startswith('X'):
              self.log(logging.WARNING, "%s: currency found with no base:\n%s", self.name, rate)